The 3rd-Generation Partnership Project (3GPP) is continuing development of a next-generation wireless communication system in its Long-Term Evolution (LTE) initiative. In particular, 3GPP work is ongoing for defining specifications for a so-called Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
The 3GPP RAN2 working group has defined a Discontinuous Reception (DRX) mechanism in the Medium Access Control (MAC) protocol specifications for LTE systems, which are currently documented as “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification (Release 8),” 3GPP TS 36.321. The purpose of DRX is to reduce user equipment (UE) power consumption to save resources and extend battery life. With DRX, the UE can turn on and off reception of Layer1/Layer2 control messages while in RRC_CONNECTED state, i.e., when the UE has established a Radio Resource Control (RRC) connection with the serving network.
A central principle in DRX is that a UE's behavior depends on whether the Physical Downlink Control Channel (PDCCH), which carries UE-specific resource grants for both uplink and downlink resources, is successfully decoded by the UE. When in DRX mode, the UE is allowed to frequently stop monitoring the PDCCH, during intervals governed by several timers. A similar DRX mechanism is used for both the uplink (UL) and the downlink (DL).
Network-initiated mobility (which includes, for example, network-initiated handovers) is another aspect of Radio Resource Control. Details of Radio Resource Control for LTE systems are defined in “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource Control (RRC); Protocol specification (Release 8),” 3GPP TS 36.331. When a UE is in RRC_CONNECTED mode, i.e., once the UE has an established the RRC connection, the network controls UE mobility, deciding when the UE shall move to which cell, which may be on another frequency or even for another radio access technology (RAT). The network triggers the handover procedure based on factors including radio conditions, network loading, and the like. To facilitate mobility decisions, the network may configure the UE to perform measurement reporting, possibly including the configuration of measurement gaps, but may also initiate handover blindly, i.e., without having received measurement information from the UE.